1. Field of the Invention
The present invention relates to a lens drive and a projector comprising a lens drive, and more particularly, it relates to a lens drive capable of moving the lens position and a projector comprising this lens drive.
2. Description of the Background Art
A projector comprising a lens drive for moving the lens position is known in general. For example, International Patent Laying-Open No. WO02/016994, Japanese Patent Laying-Open No. 2-281244 (1990) and Japanese Patent Publication No. 51-30460 (1976) disclose such projectors.
The aforementioned International Patent Laying-Open No. WO02/016994 discloses a zoom lens apparatus (lens drive) comprising a cylindrical zoom ring storing first and second variator lens groups supported by a variator lens frame, a compensator lens group arranged between the first and second variator lens groups and supported by a compensator lens frame, a focus lens group arranged on a position closest to an image and supported by a focus lens frame and a telecentric lens group arranged on a position farthest from the image. In this zoom lens apparatus disclosed in International Patent Laying-Open No. WO02/016994, drive pins provided on the variator lens frame, the compensator lens frame and the focus lens frame are fitted into grooves of the zoom ring. When the zoom ring is rotated about the optical axis, therefore, the drive pins move along the grooves of the zoom ring, thereby moving the respective lens groups along the optical axis. Thus, the zoom lens apparatus is zoomed.
The aforementioned Japanese Patent Laying-Open No. 2-281244 discloses a projector controlling a focus lens mounted on a lens support movable along ball screws parallel to the optical axis with a remote control commander. This projector disclosed in Japanese Patent Laying-Open No. 2-281244 transmits a signal received from the remote control commander in a photoreceptor thereof to a motor driving circuit controlling rotation of a microcomputer and a stepping motor of the projector thereby controlling rotation of the stepping motor, for moving the focus lens along the optical axis following rotation of the ball screws rotatably mounted on the stepping motor.
The aforementioned Japanese Patent Publication No. 51-30460 discloses a microfilm reader capable of adjusting the enlargement ratio of an image of a microfilm projected on a screen by moving a movable reflecting surface for reflecting the image projected from a lens for projecting the image on the screen along the optical axis with a motor thereby varying the distance between the lens and the movable reflecting surface. In this microfilm reader disclosed in Japanese Patent Publication No. 51-30460, the movable reflecting surface moves along the optical axis so that a cam surface mounted on the movable reflecting surface provides rotational motion to a cam follower mounted on a rotating member having a rotation axis parallel to the optical axis, thereby rotating a lens positioning cam having a plurality of cam grooves provided at prescribed intervals with the rotating member. Racks engaged with the cam grooves move along the cam grooves for displacing the position of the lens fixed to the racks, thereby regularly keeping a focusing state in response to the enlargement ratio of the image.
FIG. 16 is a perspective view showing the overall structure of a conventional projector 100. As shown in FIG. 16, the conventional projector 100 comprises a housing 101, a lens 102 for projecting a projected image, a cylindrical frame 103, a lens position control ring 104 rotatably mounted on the outer side of the cylindrical frame 103 coaxially with the optical axis and leg members 105 mounted on the bottom surface of the housing 101.
The lens 102 is arranged in the cylindrical frame 103 movably along the optical axis (direction A in FIG. 16). The lens position control ring 104 has a function of moving the lens 102 arranged in the cylindrical frame 103 along the optical axis (direction A in FIG. 16). Thus, the position of the lens 102 supported in the cylindrical frame 103 is controlled by rotating the lens position control ring 104 in a direction B shown in FIG. 16 in focus control or zoom control. The projected image is zoom-controlled or focus-controlled in this manner.
On the other hand, a liquid crystal projector capable of horizontally and elevationally controlling a projected image projected on a screen by adjusting the height of leg members mounted on the bottom surface is known in general, as disclosed in Japanese Patent Laying-Open No. 2000-241875, for example. In the liquid crystal projector disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-241875, inclination of the liquid crystal projector is changed by rotating a rotating knob mounted on a side surface of the liquid crystal projector thereby vertically expanding/contracting telescopic legs mounted on the bottom surface of the liquid crystal projector.
In the conventional projector 100 shown in FIG. 16, however, an operator must manually rotate the lens position control ring 104 arranged coaxially with the optical axis in focus control or zoom control, to disadvantageously project a shadow of his/her hand on the projected image. Consequently, it is disadvantageously difficult to focus-control and zoom-control the projected image.
In the zoom lens apparatus disclosed in the aforementioned International Patent Laying-Open No. WO02/016994, an operator must manually rotate the zoom ring arranged coaxially with the optical axis in zoom control, to disadvantageously project a shadow of his/her hand on a projected image. Consequently, it is disadvantageously difficult to zoom-control the projected image.
The projector disclosed in the aforementioned Japanese Patent Laying-Open No. 2-281244 must be provided with the stepping motor serving as a drive source and the motor driving circuit for controlling the stepping motor, and hence a mechanism for moving the focus lens is disadvantageously complicated. Consequently, a mechanism for focus-controlling and zoom-controlling the projected image is disadvantageously complicated.
The microfilm reader disclosed in the aforementioned Japanese Patent Publication No. 51-30460 must be provided with the motor serving as a drive source for moving the movable reflecting surface and the lens, and hence a mechanism for moving the lens is disadvantageously complicated. Consequently, a mechanism for focus-controlling and zoom-controlling the projected image is disadvantageously complicated.
In the liquid crystal projector disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-241875, an operator must manually rotate a lens position control ring (zoom ring or the like) arranged coaxially with the optical axis in focus control or zoom control similarly to the projector 100 shown in FIG. 16 in general, to disadvantageously project a shadow of his/her hand on the projected image, although this is not described. Consequently, it is disadvantageously difficult to focus-control and zoom-control the projected image.